The present invention concerns a pressure amplifier, including a low pressure inlet for supplying medium at low pressure, a low pressure piston with a first operational area and at least one high pressure piston with a second operational area, the second area being smaller than the first area, and at least one high pressure outlet.
This type of pressure amplifier is particularly used in hydraulic circuits, where the hydraulic pump integrated in the system cannot yield sufficiently high pressure for all applications. For a part of the hydraulic circuit it is not desirable either to operate with a hydraulic medium under such high pressure, since this make demands on the design of the hydraulic lines, joints between lines and the elements such as joints, valves, check valves etc., which do not necessarily need to be dimensioned for high pressure. Thus, a cost factor is also involved for making so low pressure in so large part of the hydraulic circuit as possible, and by inserting pressure amplifiers providing a high pressure where necessary.
In connection with the present invention, the terms low pressure and high pressure are used. As the principles underlying the invention are equally applicable at different pressures, low and high pressure, respectively, are only to be understood so that the two media have different (or same) pressure.
Furthermore, within the technical field it is commonly known how check valves are functioning, as well as the provision of return ducts, medium reservoirs, and the like, to the required extent are regarded as a matter of course for the skilled in the art. To the extent they are integrated in the apparatus and the system, respectively, and are not used directly in connection with the basically new and inventive principle of the invention, these are omitted to wide extent for the sake of clarity.
The medium that drives or is set under pressure and which is used in connection with the present invention is often hydraulic oil, but may be any other kind of liquid, including particularly water or a gas which is found suitable for use in this type of systems. Furthermore, the system and the pressure amplifier may be used by gases, including particularly air, as the pressure amplifier and the system in its structure are configured so that the possible compressibility of the gases does not have any influence on the function of the pressure amplifier.
Pressure amplifiers of the kind mentioned above are particularly used in hydraulic circuits, including particularly in cranes, trenchers, excavators, forklift trucks or corresponding machines, where great force is to be applied for lifting or moving material. For the operator of these machines, it is very desirable to dose the force to the work tools as accurately as possible. Another important aspect is to utilise the applied energy the most possible, i.e. to design a pressure amplifier and a pressure amplifier system with a minimal loss of pressure.
In a known pressure amplifier, as e.g. described in WO 8607118, is known a double acting pressure amplifier in which a central double-acting piston device provided within the pressure amplifier cylinder displaces a pre-selector that acts as a kind of servomechanism for a changeover valve, whereby liquid is continually allowed at low pressure by pushing on the low pressure pistons, so that the latter actuate a high pressure piston which via a rod transmits the high pressure to a possible actuator. The pre-selector is following the movement of the low pressure pistons slidingly, after which the valve opening is continually changed, so that at the middle of the stroke of the piston there will be fully open for the valve, whereby the opening, concurrently with the low pressure piston reaching the end of its stroke, will close more and more and thereby throttle down the intake of low pressure medium. Besides, there is provided a large number of springs, unions, and liquid ducts in and around the cylinder jacket, which otherwise co-operate with a number of sealing rings and screwed in shafts for providing low pressure liquid on the correct side of the low pressure pistons, so that these will be actuated for pressing the high pressure piston forwards for providing higher pressure.
In general, for this type of pressure amplifiers it applies that it is the effective operational area of the low pressure piston relative to the effective area of the high pressure piston that indicate the actual pressure amplification factor. For incompressible media, in theory the pressure amplification factor is directly proportional with the ratio between the two above mentioned areas. Actually, by a pressure amplifier as specified in WO 8607118 there will occur a relatively great energy loss in connection with supply of low pressure oil, as the oil is used for controlling the changeover valve, whereby losses arise in supply and relief ducts, as well as the shifting of the valve causes a pressing back and/or consumption of oil, whereby in practice a very substantial energy loss arises.
It is thus the purpose of the invention to provide a liquid or gas driven pressure amplifier that utilises all of the incoming energy for work energy.
Besides, it is a purpose to provide a pressure amplifier that does not have space demanding differential areas, whereby the entire operational area on the side operating at any time is utilised 100%, so that the energy from the drive medium is deposited as kinetic energy when moving the main piston. The other side of the main piston is simultaneously connected to a tank so that no overpressure is to be overcome.
Furthermore, the invention has the purpose of providing a changeover valve which becomes activated by the movement of the main piston in such a way that a possible flow loss and thereby pressure loss is thereby minimised. In the same connection, it is important to control the changeover valve under all conditions so that the pressure amplifier, at low as well as high operational frequencies and by rapid pressure changes will function with great certainty. This is particularly interesting where the pressure amplifier is to operate at a high rate, i.e. many directional changes per minute.
It is thus a further purpose of the invention to provide a pressure amplifier that via its construction becomes cheaper and more compact than the hitherto known amplifiers, simultaneously with being provided greater power and greater reliability.